Fastener and heat sink assembly having the same

Abstract

A fastener includes a fastener post, a sleeve, a nut and an elastic element. The fastener post includes a shaft, a tapered portion and a threaded portion. The sleeve includes a smooth portion and a clamp portion having a number of resilient strips. The nut is threaded onto the threaded portion. The elastic element is disposed around the sleeve and compressed between the nut and an ear of a heat sink to generate a resilient force. The resilient force moves the tapered portion of the fastener post into the sleeve such that the strips of the clamp portion of the sleeve are tilted outwardly to tightly abut against a bottom of a printed circuit board on which the heat sink is mounted.

1. A fastener for securing a heat sink to a printed circuit board, comprising:
 a fastener post comprising a shaft and a tapered portion, the tapered portion extending from an end of the shaft, a diameter of the tapered portion gradually increasing along a direction away from the shaft, with a threaded portion formed on another end of the shaft opposite to the tapered portion; 
 a sleeve capable of receiving the fastener post therein, the sleeve comprising a smooth portion and a clamp portion corresponding to the tapered portion of the fastener post, the clamp portion comprising a plurality of resilient strips spaced from each other, and each of the resilient strips having a free end away from the smooth portion; 
 a nut configured to be threaded onto the threaded portion; and 
 an elastic element disposed around the sleeve, 
 wherein, when the nut is threaded to compress the elastic element, resilient force generated by the compressed elastic element impels the tapered portion of the fastener post into the sleeve such that the strips of the clamp portion of the sleeve tilted outwardly. 
 
     
     
       2. The fastener of  claim 1 , wherein the shaft, the tapered portion and the threaded portion are aligned along a same axis. 
     
     
       3. The fastener of  claim 2 , wherein an inner diameter of the smooth portion is less than an outer diameter of a bottom end of the tapered portion. 
     
     
       4. The fastener of  claim 3 , wherein a plurality of ridges protrudes from an outer surface of the tapered portion and longitudinally extends from a top end of the tapered portion to the bottom end of the tapered portion. 
     
     
       5. The fastener of  claim 4 , wherein a length of each ridge is equal to or less than a distance on the outer surface of the tapered portion between the top end and the bottom end of the tapered portion. 
     
     
       6. The fastener of  claim 4 , wherein the ridges radiate downwardly and outwardly relative to an axis of the tapered portion and are equidistantly spaced from each other. 
     
     
       7. The fastener of  claim 4 , wherein each two adjacent ridges cooperatively define a recess therebetween receiving a corresponding strip of the clamp portion of the sleeve. 
     
     
       8. A heat sink assembly, comprising:
 a printed circuit board (PCB) defining a first mounting hole therein; 
 a heat sink defining a second mounting hole therein; and 
 a fastener comprising:
 a sleeve extending through the first mounting hole and the second mounting hole, the sleeve comprising a smooth portion and a clamp portion, the clamp portion comprising a plurality of resilient strips spaced from each other, and each of the resilient strips having a free end away from the smooth portion; 
 a fastener post comprising a shaft and a tapered portion, the tapered portion extending from an end of the shaft, a diameter of the tapered portion gradually increasing along a direction away from the shaft, a threaded portion being formed on another end of the shaft opposite to the tapered portion, the shaft extending through the sleeve with the tapered portion thereof engaging the clamp portion of the sleeve and the threaded portion beyond the smooth portion of the sleeve; 
 a nut threading on the threaded portion; and 
 an elastic element disposed around the sleeve and compressed between the nut and the heat sink, wherein the compressed elastic element provides a resilient force to the nut to move the tapered portion of the fastener post into the sleeve such that the strips of the clamp portion of the sleeve are tilted outwardly to thereby abut the PCB. 
 
 
     
     
       9. The heat sink assembly of  claim 8 , wherein the shaft, the tapered portion, and the threaded portion are aligned along a same axis. 
     
     
       10. The heat sink assembly of  claim 9 , wherein an inner diameter of the smooth portion is less than an outer diameter of a bottom end of the tapered portion. 
     
     
       11. The heat sink assembly of  claim 10 , wherein a plurality of ridges protrudes from an outer surface of the tapered portion and longitudinally extends from a top end of the tapered portion to the bottom end of the tapered portion. 
     
     
       12. The heat sink assembly of  claim 11 , wherein a length of each ridge is equal to or less than a distance on the outer surface of the tapered portion between the top end and the bottom end of the tapered portion. 
     
     
       13. The heat sink assembly of  claim 11 , wherein the ridges radiate downwardly and outwardly relative to an axis of the tapered portion and are spaced equidistant from each other. 
     
     
       14. The heat sink assembly of  claim 11 , wherein each two adjacent ridges cooperatively define a recess therebetween receiving a corresponding strip of the clamp portion of the sleeve.